Optimizing power transfer to negative pressure sources in negative pressure therapy systems

ABSTRACT

Embodiments of negative pressure wound therapy systems and methods are disclosed. In one embodiment, an apparatus includes a driving circuit that supplies a driving signal to a negative pressure source to cause the negative pressure source to provide negative pressure via a fluid flow path to a wound dressing. The apparatus furthers include a controller that adjusts a frequency of the driving signal supplied by the driving circuit according to a comparison of a previous magnitude and a subsequent magnitude of the driving signal while the negative pressure source provides negative pressure. The transfer of power to the negative pressure source can thereby be tuned to maximize an amount of power transferred to the negative pressure source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalPatent Application No. PCT/EP2017/060452, filed May 3, 2017, whichclaims the benefit of U.S. Provisional Application No. 62/331,098, filedMay 3, 2016, and U.S. Provisional Application No. 62/479,588, filed Mar.31, 2017; the disclosures of which are hereby incorporated by referencein their entirety.

BACKGROUND

Embodiments of the present disclosure relate to methods and apparatusesfor dressing and treating a wound with negative or reduced pressuretherapy or topical negative pressure (TNP) therapy. In particular, butwithout limitation, embodiments disclosed herein relate to negativepressure therapy devices, methods for controlling the operation of TNPsystems, and methods of using TNP systems.

SUMMARY

In some embodiments, an apparatus for applying negative pressure to awound, the apparatus can include a source of negative pressure, adriving circuit, and a controller. The source of negative pressure canprovide negative pressure via a fluid flow path to a wound dressing. Thedriving circuit can supply a driving signal to the source of negativepressure to cause the source of negative pressure to provide negativepressure. The driving signal can have a driving signal magnitude and adriving signal frequency. The controller can, while the source ofnegative pressure is maintaining negative pressure under the wounddressing within a pressure range, iteratively and at an operatingfrequency: determine the driving signal magnitude detected at a firsttime and the driving signal magnitude detected at a second timesubsequent to the first time, compare the driving signal magnitudedetected at the first time and the driving signal magnitude detected atthe second time, in response to the driving signal magnitude detected atthe first time being less than the driving signal magnitude detected atthe second time, operate the driving circuit to increase the drivingsignal frequency, and in response to the driving signal magnitudedetected at the first time being greater than the driving signalmagnitude detected at the second time, operate the driving circuit todecrease the driving signal frequency.

The apparatus of the preceding paragraph can include one or more of thefollowing features: The controller can to operate the driving circuit sothat the driving signal frequency matches an initial frequency when thedriving circuit activates the source of negative pressure to beginproviding negative pressure, and the controller can operate the drivingcircuit to increase or decrease the driving signal frequency within afirst period of time following the driving circuit activating the sourceof negative pressure. The source of negative pressure can have amechanical resonance frequency, and the mechanical resonance frequencycan be greater than the initial frequency. The source of negativepressure can have a mechanical resonance frequency, and the mechanicalresonance frequency can be less than the initial frequency. Themechanical resonance frequency can be between 5 kHz and 100 kHz. Thefirst period of time can be between 1 msec and 1 min. The driving signalmagnitude detected at the second time in a first iteration can be usedas the driving signal magnitude detected at the first time in a seconditeration subsequent to the first iteration. The first iteration and thesecond iteration may not be separated by another iteration. Thecontroller can: operate the driving circuit to increase the drivingsignal frequency by a first amount; and operate the driving circuit todecrease the driving signal frequency by a second amount. The firstamount can be the same as the second amount. The first amount can bedifferent from the second amount. The first amount or the second amountcan vary over time. The first amount or the second amount can beconstant over a second period of time while the source of negativepressure is maintaining negative pressure under the wound dressingwithin the pressure range. The second period of time can be between 10sec and 10 min. The first amount or the second amount can be between 1Hz and 1000 Hz. The operating frequency can vary over time. Theoperating frequency can be constant over a third period of time whilethe source of negative pressure is maintaining negative pressure underthe wound dressing within the pressure range. The third period of timecan be between 10 sec and 10 min. The operating frequency can be between0.1 Hz and 100 Hz. The source of negative pressure can include apiezoelectric pump. The source of negative pressure can include amicropump. The source of negative pressure can perform negative pressurewound therapy when negative pressure under the wound dressing ismaintained within the pressure range. The apparatus can further includethe wound dressing, and the source of negative pressure can be disposedon or within the wound dressing. The driving circuit can include anH-bridge circuit. The controller can further provide a control signal tothe driving circuit, and the controller can control the driving signalby adjusting a pulse width modulation of the control signal. The drivingcircuit can supply the driving signal by supplying an electrical voltageacross input terminals of the source of negative pressure via thecoupling circuit, and the electrical voltage can range from greater than−50 V to less than +50 V. The driving signal can include an electricalcurrent.

A method of operating, using, or manufacturing the apparatus of thepreceding two paragraphs is also disclosed.

In some embodiments, a method of operating a negative pressure woundtherapy apparatus is disclosed. The method can include: supplying adriving signal at a first time and at a second time to a source ofnegative pressure, the driving signal having a driving signal magnitudeand a driving signal frequency, the second time being subsequent to thefirst time; providing negative pressure via a fluid flow path to a wounddressing with the source of negative pressure responsive to the drivingsignal; determining the driving signal magnitude at the first time andthe driving signal magnitude at the second time; comparing the drivingsignal magnitude at the first time and the driving signal magnitude atthe second time; in response to the driving signal magnitude at thefirst time being less than the driving signal magnitude at the secondtime, increasing the driving signal frequency supplied to the source ofnegative pressure; and in response to the driving signal magnitude atthe first time being greater than the driving signal magnitude at thesecond time, decreasing the driving signal frequency supplied to thesource of negative pressure.

The method of the preceding paragraph can include one or more of thefollowing features: The increasing the driving signal frequency caninclude increasing the driving signal frequency by a first amount; andthe decreasing the driving signal frequency can include decreasing thedriving signal frequency by a second amount. The first amount can be thesame as the second amount. The first amount can be different from thesecond amount. The first amount or the second amount can be between 1 Hzand 1000 Hz. The source of negative pressure can include a piezoelectricpump. The source of negative pressure can include a micropump. Thedriving signal can include an electrical current.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the present disclosure will be apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings of which:

FIG. 1 illustrates a negative pressure therapy system according to someembodiments.

FIGS. 2A and 2B respectively illustrate a side view and top view of anegative pressure therapy system according to some embodiments, such asthe negative pressure therapy system of FIG. 1.

FIG. 3 illustrates a block diagram of electrical communication pathsbetween a power source, control circuitry, and negative pressure source,as well as components of the control circuitry, according to someembodiments.

FIGS. 4A and 4B illustrate simplified circuit components of a drivingcircuit according to some embodiments.

FIG. 4C illustrates circuit components of a driving circuit according tosome embodiments.

FIG. 5 illustrates circuit components of a coupling circuit according tosome embodiments.

FIG. 6 illustrates a therapy control process performable by a negativepressure therapy system according to some embodiments.

DETAILED DESCRIPTION

The present disclosure relates to methods and apparatuses for dressingand treating a wound with reduced pressure therapy or topical negativepressure (TNP) therapy. In particular, but without limitation,embodiments of this disclosure relate to negative pressure therapyapparatuses, methods for controlling the operation of TNP systems, andmethods of using TNP systems. The methods and apparatuses canincorporate or implement any combination of the features describedbelow.

Many different types of wound dressings are known for aiding in thehealing process of a human or animal. These different types of wounddressings include many different types of materials and layers, forexample, gauze, pads, foam pads or multi-layer wound dressings. TNPtherapy, sometimes referred to as vacuum assisted closure, negativepressure wound therapy, or reduced pressure wound therapy, can be abeneficial mechanism for improving the healing rate of a wound. Suchtherapy is applicable to a broad range of wounds such as incisionalwounds, open wounds and abdominal wounds or the like.

TNP therapy can assist in the closure and healing of wounds by reducingtissue oedema, encouraging blood flow, stimulating the formation ofgranulation tissue, removing excess exudates, and reducing bacterialload and thus, infection to the wound. Furthermore, TNP therapy canpermit less outside disturbance of the wound and promote more rapidhealing.

As is used herein, reduced or negative pressure levels, such as −X mmHg,represent pressure levels that are below atmospheric pressure, whichtypically corresponds to 760 mmHg (or 1 atm, 29.93 inHg, 101.325 kPa,14.696 psi, etc.). Accordingly, a negative pressure value of −X mmHgreflects pressure that is X mmHg below atmospheric pressure, such as apressure of (760−X) mmHg. In addition, negative pressure that is “less”or “smaller” than −X mmHg corresponds to pressure that is closer toatmospheric pressure (e.g., −40 mmHg is less than −60 mmHg). Negativepressure that is “more” or “greater” than −X mmHg corresponds topressure that is further from atmospheric pressure (e.g., −80 mmHg ismore than −60 mmHg).

Overview

Control circuitry of a TNP apparatus can supply a driving signal (forexample, an electrical current) to a negative pressure source and vary afrequency of the driving signal (for instance, an AC waveform frequencyof the electrical current). By varying the frequency over time (forexample, to match a mechanical resonance frequency of a piezoelectricpump of the negative pressure source), the control circuitry can tunethe transfer of power to the negative pressure source to maximize anamount of power transferred to the negative pressure source. As aresult, the TNP apparatus can automatically accommodate for componentvariances attributable to, for example, operating temperatures ormanufacturing differences and operate the negative pressure source at anoptimum or near optimum power level. In some implementations, theresonance frequency of the negative pressure source can vary in responseto, for example, variations in temperature, humidity, and the like.

Reduced Pressure Therapy Systems and Methods

FIG. 1 illustrates a negative pressure therapy system 100 that includesa TNP apparatus 11 and a wound 14. The TNP apparatus 11 can be used totreat the wound 14. The TNP apparatus 11 can include control circuitry12A, memory 12B, a negative pressure source 12C, a user interface 12D, apower source 12E, a first pressure sensor 12F, and a second pressuresensor 12G that are configured to electrically communicate with oneanother. In addition, the TNP apparatus 11 can include a wound dressing13. The power source 12E can provide power to one or more components ofthe TNP apparatus 11.

One or more of the control circuitry 12A, memory device 12B, negativepressure source 12C, user interface 12D, power source 12E, firstpressure sensor 12F, and second pressure sensor 12G can be integralwith, incorporated as part of, attached to, or disposed in the wounddressing 13. The TNP apparatus 11 can accordingly be considered to haveits control electronics and pump on-board the wound dressing 13 ratherthan separate from the wound dressing 13.

The control circuitry 12A can include one or more controllers (forexample, a microcontroller or microprocessor), activation circuits,boost converters, current limiters, feedback conditioning circuits, andH-bridge inverters. The control circuitry 12A can control the operationsof one or more other components of the TNP apparatus 11 according atleast to instructions stored in the memory device 12B. The controlcircuitry 12A can, for instance, control operations of and supply ofnegative pressure by the negative pressure source 12C.

The negative pressure source 12C can include a pump, such as, withoutlimitation, a rotary diaphragm pump or other diaphragm pump, apiezoelectric pump, a peristaltic pump, a piston pump, a rotary vanepump, a liquid ring pump, a scroll pump, a pump operated by apiezoelectric transducer, or any other suitable pump or micropump or anycombinations of the foregoing. The pump can include an actuator drivenby a source of energy, such as electrical energy, mechanical energy, andthe like. For example, the actuator can be an electric motor, apiezoelectric transducer, a voice coil actuator, an electroactivepolymer, a shape-memory alloy, a comb drive, a hydraulic motor, apneumatic actuator, a screw jack, a servomechanism, a solenoid actuator,a stepper motor, a plunger, a combustion engine, and the like. In someembodiments, the negative pressure source 12C can supply negativepressure by converting electrical energy to mechanical energy withoutconverting the electrical energy to magnetic energy. In suchembodiments, the pump can have a different impact when electricallycoupled to one or more other components of the control circuitry 12Athan if the negative pressure source 12C supplied negative pressure byconverting the electrical energy to the magnetic energy and then to themechanical energy.

The user interface 12D can include one or more elements that receiveuser inputs or provide user outputs to a patient or caregiver. The oneor more elements that receive user inputs can include buttons, switches,dials, touch screens, or the like, and the one or more elements thatprovide user outputs can include activation of a light emitting diode(LED) or one or more pixels of the display or activation of a speaker orthe like. In one example, the user interface 12D can include a switch toreceive user inputs (for instance, a negative pressure activation ordeactivation input) and two LEDs to indicate an operating status (forexample, functioning normally, under fault condition, or awaiting userinput) of the TNP apparatus 11.

The first pressure sensor 12F can be used to monitor pressure underneaththe wound dressing 13, such as pressure in a fluid flow path connectingthe negative pressure source 12C and the wound 14, pressure at the wound14, or pressure in the negative pressure source 12C. The second pressuresensor 12G can be used to monitor pressure external to the wounddressing 13. The pressure external to the wound dressing can beatmospheric pressure; however, the atmospheric pressure can varydepending on, for instance, an altitude of use or pressurizedenvironment in which the TNP apparatus 11 may be used.

The control circuitry 12A can control the supply of negative pressure bythe negative pressure source 12C according at least to a comparisonbetween the pressure monitored by the first pressure sensor 12F and thepressure monitored by the second pressure sensor 12G.

The wound dressing 13 can include a wound contact layer, a spacer layer,and an absorbent layer. The wound contact layer can be in contact withthe wound 14. The wound contact layer can include an adhesive on thepatient facing side for securing the dressing to the skin surroundingthe wound 14 or on the top side for securing the wound contact layer toa cover layer or other layer of the wound dressing 13. In operation, thewound contact layer can provide unidirectional flow so as to facilitateremoval of exudate from the wound while blocking or substantiallypreventing exudate from returning to the wound 14. The spacer layer canassist in distributing negative pressure over the wound site andfacilitating transport of wound exudate and fluids into the wounddressing 13. Further, the absorbent layer can absorb and retain exudateaspirated from the wound 14.

The control circuitry 12A can monitor the activity of the negativepressure source 12C, which may include monitoring a duty cycle of thenegative pressure source 12C (for example, the duty cycle of theactuator of the negative pressure source). As is used herein, the “dutycycle” can reflect the amount of time the negative pressure source 12Cis active or running over a period of time. In other words, the dutycycle can reflect time that the negative pressure source 12C is in anactive state as a fraction of total time under consideration. Duty cyclemeasurements can reflect a level of activity of the negative pressuresource 12C. For example, the duty cycle can indicate that the negativepressure source 12C is operating normally, working hard, workingextremely hard, etc. Moreover, the duty cycle measurements, such asperiodic duty cycle measurements, can reflect various operatingconditions, such as presence or severity of leaks, rate of flow of fluid(for instance, air, liquid, or solid exudate, etc.) aspirated from awound, or the like. Based on the duty cycle measurements, such as bycomparing the measured duty cycle with a set of thresholds (forinstance, determined in calibration), the controller can execute or beprogrammed to execute algorithms or logic that control the operation ofthe system. For example, duty cycle measurements can indicate presenceof a high leak, and the control circuitry 12A can be programmed toindicate this condition to a user (for instance, patient, caregiver, orphysician) or temporarily suspend or pause operation of the source ofnegative pressure in order to conserve power.

When the TNP apparatus 11 may be used to treat the wound 14, the wounddressing 13 can create a substantially sealed or closed space around thewound 13 and under the wound dressing 13, and the first pressure sensor12F can periodically or continuously measure or monitor a level ofpressure in this space. The control circuitry 12A can control the levelof pressure in the space between a first negative pressure set pointlimit and at least a second negative pressure set point limit. In someinstances, the first set point limit can be approximately −70 mmHg, orfrom approximately −60 mmHg or less to approximately −80 mmHg or more.In some instances, the second set point limit can be approximately −90mmHg, or from approximately −80 mmHg or less to approximately −100 mmHgor more.

FIG. 2A illustrates a side view of a negative pressure therapy system200, and FIG. 2B illustrates a top view of the negative pressure therapysystem 200. The negative pressure therapy system 200 can be an exampleimplementation of the negative pressure therapy system 100.

In the negative pressure therapy system 200, the wound dressing 13 ofthe TNP apparatus 11 is shown as attached to the wound 14. Arrows depictthe flow of air through the wound dressing 13 and wound exudate from thewound 14. The TNP apparatus 11 can include an air exhaust 26 and acomponent area 25, such as a components housing or storage area forcomponents of the TNP apparatus 11 like one or more of the controlcircuitry 12A, memory device 12B, negative pressure source 12C, userinterface 12D, power source 12E, first pressure sensor 12F, and secondpressure sensor 12G.

The user interface 12D of the negative pressure therapy system 200 caninclude a switch 21 (such as a dome switch), a first indicator 23 (suchas a first LED), and a second indicator 24 (such as a second LED). Theswitch 21 can receive a negative pressure activation or deactivationuser input (for example, such as receiving the activation ordeactivation user input in response to depression of the switch 21 for aperiod of time, like from between 0.5 seconds and 5 seconds). The firstindicator 23 and the second indicator 24 can indicate an operatingstatus like functioning normally, under fault condition, or awaitinguser input. In some implementations, the switch 21 can couple to a powersupply connection of the negative pressure source 12C or the controlcircuitry 12A or an enable signal of the negative pressure source 12C orthe control circuitry 12A to activate or deactivate supply of negativepressure or disable supply of negative pressure.

Component parts of the wound dressing 13 of the negative pressuretherapy system 200 are illustrated to include an airlock layer 27, anabsorbing layer 28, and a contact layer 29. The airlock layer 27 canenable air flow. The absorbing layer 28 can absorb wound exudate. Thecontact layer 29 can be soft and include silicon and be used to couplethe TNP apparatus 11 to the patient.

FIG. 3 illustrates a block diagram 300 depicting example electricalcommunication paths between the power source 12D, control circuitry 12A,and negative pressure source 12C, as well as example components of thecontrol circuitry 12A including a controller 31, a current limiter 32, adriving circuit 33, a feedback conditioner 34, and the coupling circuit35. FIG. 3 shows, in particular, how the controller 31 can be used tocontrol the supply of negative pressure by the negative pressure source12C.

The power source 12D can include one or more power supplies, such asbatteries (such as, multiple 3 V batteries) or a connection to mainspower, to provide power for one or more components of the TNP apparatus11. The power source 12D can, for instance, provide electrical currentand voltage to the current limiter 32. The voltage output by the powersource 12D can be around 30 V, such as 29 V±1 V, in someimplementations. The power source 12D can additionally includecircuitry, such as a boost converter, to control the electrical currentand voltage provided to the current limiter 32.

The current limiter 32 can serve to limit or clamp the current at amaximum current level, such as at 100 mA, 250 mA, 466 mA, 500 mA, or 1A, to limit potential fault current through the driving circuit 33 andthe negative pressure source 12C. Under normal operation (for example,in most or some instances), the current limiter 32 may not operate tolimit current or voltage.

The current limiter 32 can provide electric current and voltage to thedriving circuit 33. The driving circuit 33 can include an H-bridgecircuit composed of multiple switches. The H-bridge can be constructedto operate as an H-bridge inverter. The driving circuit 33 can providefeedback to the controller 31 via the feedback conditioner 34. Thefeedback conditioner 34 can be used, for instance, to condition currentfeedback information from the driving circuit 33 before the currentfeedback information is provided to the controller 31. In one example,the feedback conditioner 34 can include a low-pass filter (which can,for example, include active circuit components) to filter switchingnoise caused by the switching of one or more switches of the drivingcircuit 33. The controller 31 can, in turn, control the operations ofthe driving circuit 33 based on the feedback, in some instances.

The controller 31 can control operations of the driving circuit 33, andin turn the negative pressure source 12C, by outputting one or morecontrol signals via one or more outputs of the controller 31 to one ormore inputs of the driving circuit 33. For example, the controller 31can output a first control signal via a first output O1 of thecontroller 31 to a first input I1 of the driving circuit 33 and a secondcontrol signal via a second output O2 of the controller 31 to a secondinput I2 of the driving circuit 33. The controller 31 can vary a pulsewidth modulation (PWM) of the first and second control signals to adjustan electrical current and voltage provided by the driving circuit 33 tothe coupling circuit 35 and then to the negative pressure source 12C. Inone implementation, the driving circuit 33 can include an H-bridge, andthe controller 31 can generate the first and second control signals tocause the H-bridge to output electrical currents and voltages having asquare waveform (such as about ±30 V) with a frequency (such as 18 kHzto 24 kHz or about 21 kHz) and a duty cycle or ratio (such as about 50%)via a first output O1 of the driving circuit 33 and a second output O2of the driving circuit 33.

The driving circuit 33 can control supply negative pressure by thenegative pressure source 12C by providing electrical currents andvoltages to the negative pressure source 12C (for example, to theactuator of the negative pressure source 12C) via the coupling circuit35. The driving circuit 33 can, for instance, output electrical currentsvia the first and second outputs O1 and O2 of the driving circuit 33 toa first input I1 of the coupling circuit 35 and a second input I2 of thecoupling circuit 35. The coupling circuit 35 can, in turn, outputelectrical currents via a first output O1 of the coupling circuit 35 anda second output O2 of the coupling circuit 35 to a first input I1 of thenegative pressure source 12C and a second input I2 of the negativepressure source 12C. The electrical currents output by the drivingcircuit 33 and the coupling circuit 35 can notably be considered toresult in positive charge flowing away from the driving circuit 33 (thatis, sourcing of electrical current by the driving circuit 33) or towardthe driving circuit 33 (that is, sinking of electrical current by thedriving circuit 33).

The coupling circuit 35 can serve to limit a rate of change over time ofthe current supplied by the driving circuit 33 to the negative pressuresource 12C or limit a rate of change over time of a voltage across firstand second inputs I1 and I2 of the negative pressure source 12C. Thecoupling circuit 35 can have an inductive reactance greater than 1 mΩ, 5mΩ, 10 mΩ, 50 mΩ, 100 mΩ, 500 mΩ, 750 mΩ at an operating frequency of 1kHz. In some embodiments, the coupling circuit 35 can include passivecircuit elements and not include active circuit elements, but in otherembodiments, the coupling circuit 35 can include one or both of passivecircuit elements and active circuit elements.

FIGS. 4A and 4B illustrate example simplified circuit components of thedriving circuit 33. As can be seen from FIGS. 4A and 4B, the drivingcircuit 33 can be composed of at least four switches, including a firstswitch S1, a second switch S2, a third switch S3, and a fourth switch S4but together form an H-bridge. The first and fourth switches S1 and S4can be closed at the same time and the second and third switches S2 andS3 can be opened at the same time, as shown in FIG. 4A, to supply afirst current i1 in a first direction through the coupling circuit 35and the negative pressure source 12C. The second and third switches S2and S3 can be closed at the same time and the first and fourth switchesS1 and S4 can be opened at the same time, as shown in FIG. 4B, to supplya second current i2 in a second direction through the coupling circuit35 and the negative pressure source 12C. The first direction can beopposite the second direction.

FIG. 4C illustrates example circuit components of the driving circuit 33(an H-bridge in the illustrated example) that include a resistor 42. Inthe example circuit components shown in FIG. 4C, the electrical currentthat travels through the resistor 42 can be the same or substantiallythe same as the electrical current that travels through the couplingcircuit 35 and the negative pressure source 12C (for example, theactuator of the negative pressure source 12C). As a result, a feedbackprovided to the feedback conditioner 34 can, for instance, be a voltagelevel or drop across the resistor 42, which can be proportional to theelectrical current that travels through the resistor 42, as well as theelectrical current that travels through the coupling circuit 35 and thenegative pressure source 12C. Resistor 42 thus can be used to measureone or more properties of the electrical current, such as a magnitude,that is fed to the negative pressure source 12C via the coupling circuit35, such as via an inductor of the coupling circuit 35 like an inductor52 described with respect to FIG. 5. The resistor 42 can be coupled to alow-pass filter, as described herein.

FIG. 5 illustrates example circuit components of the coupling circuit35. As can be seen from FIG. 5, the coupling circuit 35 can include theinductor 52 electrically coupled in series between the first output O1of the driving circuit 33 and the first input I1 of the negativepressure source 12C, and a wire or an electrical short 54 electricallycoupled in series between the second output O2 of the driving circuit 33and the second input I2 of the negative pressure source 12C. Theinductor 52 can have an inductance ranging from 0.1 pH to 1000 pH, 1 μHto 100 μH, or 3 μH to 10 μH, or an inductance of about 7.5 μH. Theinductor 52 can have a maximum current rating of greater than 0.25 A,0.5 A, 0.75 A, 1 A, or 1.25 A. The inductor 52 can be used to opposerapid changes in a voltage or current supplied to drive the negativepressure source 12C.

In another embodiment, the coupling circuit 35 can include a first wireor a first electrical short electrically coupled in series between thefirst output O1 of the driving circuit 33 and the first input I1 of thenegative pressure source 12C, and a second wire or a second electricalshort electrically coupled in series between the second output O2 of thedriving circuit 33 and the second input I2 of the negative pressuresource 12C.

In yet another embodiment, the coupling circuit 35 can include a firstwire or a first electrical short electrically coupled in series betweenthe first output O1 of the driving circuit 33 and the first input I1 ofthe negative pressure source 12C, and an inductor (such as the inductor52) electrically coupled in series between the second output O2 of thedriving circuit 33 and the second input I2 of the negative pressuresource 12C.

In yet a further embodiment, the coupling circuit 35 can include a firstinductor (such as the inductor 52) electrically coupled in seriesbetween the first output O1 of the driving circuit 33 and the firstinput I1 of the negative pressure source 12C, and a second inductor(such as the inductor 52) electrically coupled in series between thesecond output O2 of the driving circuit 33 and the second input I2 ofthe negative pressure source 12C.

In certain implementations, one or more active elements can be used inplace of or in addition to one or more inductors.

FIG. 6 illustrates a therapy control process 600 performable by anapparatus, such as the TNP apparatus 11. For convenience, the therapycontrol process 600 is described in the context of the TNP apparatus 11,but may instead be implemented in other systems described herein or byother computing systems not shown. The therapy control process 600 canbe an iterative process by which a TNP apparatus tunes the transfer ofpower (for example, by adjusting parameters of a driving signal) to anegative pressure source to maximize an amount of power transferred tothe negative pressure source and thereby improve the efficiency (which,for example, can be measured by a more efficient power consumption).

The therapy control process 600 may begin within a period of time afterstartup of the TNP apparatus, such as within 0.001, 0.01, 0.1, 0.5, 1,2, or 5 minutes of starting supply of pressure with the negativepressure source. The therapy control process 600 can initiate with aparticular driving signal energy having an initial magnitude and aninitial frequency (for example, an electrical current having an initialcurrent magnitude and an initial current frequency) already beingprovided to negative pressure source. The initial frequency can be lessthan or greater than a mechanical resonant frequency (for example, whichcan be 1, 5, 10, 25, 50, 100, 200, 500, and 1000 kHz) of the negativepressure source.

At block 61, the therapy control process 600 can determine a currentmagnitude of an electrical current at a previous time and at a nexttime. For example, the controller 31 can determine a current magnitudeof an electrical current supplied by the driving circuit 33 to thecoupling circuit 35 and the negative pressure source 12C at a previoustime and at a next time. The previous time can be a time prior to thenext time. The previous time can, for instance, be a time during animmediately previous iteration to the next time or a time during two ormore iterations previous to the next time. The controller 31 candetermine the current magnitude (or a value indicative thereof) from thefeedback provided by the feedback conditioner 34.

At block 62, the therapy control process 600 can compare the currentmagnitude at the previous time and the next time. For example, thecontroller 31 can compare the current magnitude of the electricalcurrent supplied by the driving circuit 33 at the previous time and thecurrent magnitude of the electrical current supplied by the drivingcircuit 33 at the next time.

At block 63, the therapy control process 600 can determine if thecurrent magnitude at the previous time is less than at the next time.For example, the controller 31 can determine if the current magnitude ofthe electrical current supplied by the driving circuit 33 at theprevious time is less than the current magnitude of the electricalcurrent supplied by the driving circuit 33 at the next time.

If the result at block 63 is yes, the therapy control process 600 can atblock 64 increase a current frequency of the electrical current. Forexample, the controller 31 can increase the frequency of the electricalcurrent supplied by the driving circuit 33 by an increase amount (forexample, 1, 3, 5, 10, 30, 50, 70, 100, 200, 300, 500, 700, 850, 1000,2000, or 5000 Hz). If the result at block 63 is no, the therapy controlprocess 600 can at block 65 decrease a current frequency of theelectrical current. For example, the controller 31 can at block 65decrease the frequency of the electrical current supplied by the drivingcircuit 33 by a decrease amount (for example, 1, 3, 5, 10, 30, 50, 70,100, 200, 300, 500, 700, 850, 1000, 2000, or 5000 Hz). The increaseamount and decrease amount can be the same or different from one anotherin some instances or implementations. Moreover, the increase amount ordecrease amount can vary over time or be constant for a period of time(for example, 1, 3, 10, 30, or 60 seconds or 1, 3, 5, 10, or 30minutes).

At block 66, the therapy control process 600 can determine whether toreturn to block 61 or end. For example, the controller 31 can determinewhether to repeat the therapy control process 600, such as by repeatingthe therapy control process 600 with a repeat frequency (for example,that may be 0.01, 0.03, 0.1, 0.3, 0.5, 1, 3, 5, 10, 30, 50, 100, 300,500, 1000, 3000, or 5000 Hz and vary or be constant over a period oftime, such as 1, 3, 10, 30, or 60 seconds or 1, 3, 5, 10, or 30 minutes)or in response to a triggering event (such as a detected change intemperate of the TNP apparatus measured by a temperature sensor).

Through the therapy control process 600, a mechanical resonant frequencyof the negative pressure source can be “searched” (for instance,continuously or periodically) during provision of therapy by attemptingto adjust the initial frequency to more closely match the mechanicalresonant frequency. The mechanical resonant frequency thus may not beknown in advance of operating the TNP apparatus or known with a highprecision or accuracy, and yet the frequency of the energy provided tothe negative pressure source can be made to substantially match themechanical resonant frequency. Moreover, the frequency of the energyprovided to the negative pressure source can be made to follow themechanical resonant frequency as the mechanical resonant frequency maychange due to the changing operating conditions, which in the case ofthe negative pressure source being mounted on or within the wounddressing can include a changing temperature, duration of operation,humidity, or the like.

In some embodiments, an apparatus for applying negative pressure to awound includes a source of negative pressure, a driving circuit, asensor, and a controller. The source of negative pressure can providenegative pressure via a fluid flow path to a wound dressing placed overthe wound. The driving circuit can supply an electrical current to thesource of negative pressure to cause the source of negative pressure toprovide negative pressure. The electrical current can have a currentmagnitude and a current frequency. The sensor can detect the currentmagnitude. The controller can, while the source of negative pressure isproviding negative pressure to the wound dressing, iteratively and at afirst operating frequency: determine the current magnitude detected at aprevious time and the current magnitude detected at a next timesubsequent to the previous time; compare the current magnitude detectedat the previous time and the current magnitude detected at the nexttime; in response to the current magnitude detected at the previous timebeing less than the current magnitude detected at the next time, operatethe driving circuit to increase (or decrease) the current frequency; andin response to the current magnitude detected at the previous time beinggreater than the current magnitude detected at the next time, operatethe driving circuit to decrease (or increase) the current frequency.

The apparatus of the preceding paragraph can include one or more of thefollowing features: The controller can operate the driving circuit sothat the current frequency matches an initial frequency when the drivingcircuit activates the source of negative pressure to begin providingnegative pressure, and the controller can operate the driving circuit toincrease or decrease the current frequency within a first period of timefrom the driving circuit activating the source of negative pressure. Thesource of negative pressure can have a mechanical resonance frequency,and the mechanical resonance frequency can be greater than the initialfrequency. The source of negative pressure can have a mechanicalresonance frequency, and the mechanical resonance frequency can be lessthan the initial frequency. The source of negative pressure can have amechanical resonance frequency with one or more subharmonic or harmonicfrequencies, and the controller can operate the driving circuit toincrease or decrease the current frequency so that the current frequencyis not one of the one or more subharmonic or harmonic frequencies orremains outside of one or more frequency ranges that include the one ormore subharmonic or harmonic frequencies. The mechanical resonancefrequency can be between 5 KHz and 100 kHz, such as around 20 KHz, 22kHz, or 24 kHz or greater or less than 5 KHz and 100 kHz. The firstperiod of time can be between 1 msec and 1 min, such as around 1 msec,10 msec, 100 msec, or 1 sec or greater or less than 1 msec and 1 min.The current magnitude detected at the next time in a first iteration isthe current magnitude detected at the previous time in a seconditeration subsequent to the first iteration. The first iteration and thesecond iteration may not be separated by another iteration. Thecontroller can: operate the driving circuit to increase the currentfrequency by a first amount; and operate the driving circuit to decreasethe current frequency by a second amount. The first amount can be thesame as the second amount. The first amount can be different from thesecond amount. The first amount or the second amount can vary over time.The first amount or the second amount can be constant over a secondperiod of time while the source of negative pressure is providingnegative pressure to the wound dressing. The second period of time canbe between 10 sec and 10 min, such as around 10 sec, 1 min, or 10 min orgreater or less than 10 sec and 10 min. The first amount or the secondamount can be between 1 Hz and 1000 Hz, such as around 1 Hz, 10 Hz, 100Hz, or 1000 Hz or greater or less than 1 Hz and 1000 Hz. The firstoperating frequency can vary over time. The first operating frequencycan be constant over a third period of time while the source of negativepressure is providing negative pressure to the wound dressing. The thirdperiod of time can be between 10 sec and 10 min, such as around 10 sec,1 min, or 10 min or greater or less than 10 sec and 10 min. The firstoperating frequency can be between 0.1 Hz and 100 Hz, such as around 0.1Hz, 1 Hz, 10 Hz, or 100 Hz or greater or less than 0.1 Hz and 100 Hz.The source of negative pressure can include a piezoelectric pump. Thesource of negative pressure can be a micropump. The source of negativepressure can be disposed on or within the wound dressing. The drivingcircuit can include an H-bridge. The controller can provide a controlsignal to the driving circuit, and the controller can control theelectrical current supplied by the driving circuit by adjusting a pulsewidth modulation of the control signal. The driving circuit can supplyan electrical voltage across input terminals of the source of negativepressure via the coupling circuit, and the electrical voltage can rangefrom greater than −50 V to less than +50 V.

Other Variations

Any value of a threshold, limit, duration, etc. provided herein is notintended to be absolute and, thereby, can be approximate. In addition,any threshold, limit, duration, etc. provided herein can be fixed orvaried either automatically or by a user. Furthermore, as is used hereinrelative terminology such as exceeds, greater than, less than, etc. inrelation to a reference value is intended to also encompass being equalto the reference value. For example, exceeding a reference value that ispositive can encompass being equal to or greater than the referencevalue. In addition, as is used herein relative terminology such asexceeds, greater than, less than, etc. in relation to a reference valueis intended to also encompass an inverse of the disclosed relationship,such as below, less than, greater than, etc. in relations to thereference value. Moreover, although blocks of the various processes maybe described in terms of determining whether a value meets or does notmeet a particular threshold, the blocks can be similarly understood, forexample, in terms of a value (i) being below or above a threshold or(ii) satisfying or not satisfying a threshold.

Features, materials, characteristics, or groups described in conjunctionwith a particular aspect, embodiment, or example are to be understood tobe applicable to any other aspect, embodiment or example describedherein unless incompatible therewith. All of the features disclosed inthis specification (including any accompanying claims, abstract, anddrawings), or all of the steps of any method or process so disclosed,may be combined in any combination, except combinations where at leastsome of such features or steps are mutually exclusive. The protection isnot restricted to the details of any foregoing embodiments. Theprotection extends to any novel one, or any novel combination, of thefeatures disclosed in this specification (including any accompanyingclaims, abstract and drawings), or to any novel one, or any novelcombination, of the steps of any method or process so disclosed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of protection. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms. Furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made. Those skilled in the art willappreciate that in some embodiments, the actual steps taken in theprocesses illustrated or disclosed may differ from those shown in thefigures. Depending on the embodiment, certain of the steps describedabove may be removed, others may be added. For example, the actual stepsor order of steps taken in the disclosed processes may differ from thoseshown in the figure. Depending on the embodiment, certain of the stepsdescribed above may be removed, others may be added. For instance, thevarious components illustrated in the figures may be implemented assoftware or firmware on a processor, controller, ASIC, FPGA, ordedicated hardware. Hardware components, such as processors, ASICs,FPGAs, and the like, can include logic circuitry. Furthermore, thefeatures and attributes of the specific embodiments disclosed above maybe combined in different ways to form additional embodiments, all ofwhich fall within the scope of the present disclosure.

User interface screens illustrated and described herein can includeadditional or alternative components. These components can includemenus, lists, buttons, text boxes, labels, radio buttons, scroll bars,sliders, checkboxes, combo boxes, status bars, dialog boxes, windows,and the like. User interface screens can include additional oralternative information. Components can be arranged, grouped, displayedin any suitable order.

Although the present disclosure includes certain embodiments, examplesand applications, it will be understood by those skilled in the art thatthe present disclosure extends beyond the specifically disclosedembodiments to other alternative embodiments or uses and obviousmodifications and equivalents thereof, including embodiments which donot provide all of the features and advantages set forth herein.Accordingly, the scope of the present disclosure is not intended to belimited by the specific disclosures of preferred embodiments herein, andmay be defined by claims as presented herein or as presented in thefuture.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements, or steps. Thus, such conditional language is notgenerally intended to imply that features, elements, or steps are in anyway required for one or more embodiments or that one or more embodimentsnecessarily include logic for deciding, with or without user input orprompting, whether these features, elements, or steps are included orare to be performed in any particular embodiment. The terms“comprising,” “including,” “having,” and the like are synonymous and areused inclusively, in an open-ended fashion, and do not excludeadditional elements, features, acts, operations, and so forth. Also, theterm “or” is used in its inclusive sense (and not in its exclusivesense) so that when used, for example, to connect a list of elements,the term “or” means one, some, or all of the elements in the list.Further, the term “each,” as used herein, in addition to having itsordinary meaning, can mean any subset of a set of elements to which theterm “each” is applied.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms “approximately,”“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than 10% of, within less than 5% of, within less than 1% of, withinless than 0.1% of, and within less than 0.01% of the stated amount. Asanother example, in certain embodiments, the terms “generally parallel”and “substantially parallel” refer to a value, amount, or characteristicthat departs from exactly parallel by less than or equal to 15 degrees,10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

The scope of the present disclosure is not intended to be limited by thespecific disclosures of preferred embodiments in this section orelsewhere in this specification, and may be defined by claims aspresented in this section or elsewhere in this specification or aspresented in the future. The language of the claims is to be interpretedbroadly based on the language employed in the claims and not limited tothe examples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive.

What is claimed:
 1. An apparatus for applying negative pressure to awound, the apparatus comprising: a source of negative pressureconfigured to provide negative pressure via a fluid flow path to a wounddressing; a driving circuit configured to generate a driving signal thathas a magnitude and a frequency and provide the driving signal to thesource of negative pressure to power the source of negative pressure toprovide negative pressure, wherein the driving signal comprises anelectrical current or an electrical voltage; and a controller programmedto, while the source of negative pressure is maintaining negativepressure under the wound dressing within a pressure range, iteratively:determine the magnitude of the driving signal at a first time and asecond time subsequent to the first time, determine whether themagnitude of the driving signal at the first time is less or greaterthan the magnitude of the driving signal at the second time, in responseto determining that the magnitude of the driving signal at the firsttime is less than the magnitude of the driving signal at the secondtime, operate the driving circuit to increase the frequency of thedriving signal generated by the driving circuit, and in response todetermining that the magnitude of the driving signal at the first timeis greater than the magnitude of the driving signal at the second time,operate the driving circuit to decrease the frequency of the drivingsignal generated by the driving circuit.
 2. The apparatus of claim 1,wherein the controller is programmed to operate the driving circuit sothat the frequency of the driving signal matches an initial frequencywhen the driving circuit activates the source of negative pressure tobegin providing negative pressure, and the controller is programmed tooperate the driving circuit to increase or decrease the frequency of thedriving signal within a first period of time following the drivingcircuit activating the source of negative pressure.
 3. The apparatus ofclaim 2, wherein the source of negative pressure has a mechanicalresonance frequency, and the mechanical resonance frequency is greaterthan the initial frequency.
 4. The apparatus of claim 2, wherein thesource of negative pressure has a mechanical resonance frequency, andthe mechanical resonance frequency is less than the initial frequency.5. The apparatus of claim 4, wherein the mechanical resonance frequencyis between 5 kHz and 100 kHz.
 6. The apparatus of claim 2, wherein thefirst period of time is between 1 msec and 1 min.
 7. The apparatus ofclaim 1, wherein the magnitude of the driving signal at the second timein a first iteration is used as the magnitude of the driving signal atthe first time in a second iteration subsequent to the first iteration.8. The apparatus of claim 7, wherein the first iteration and the seconditeration are not separated by another iteration.
 9. The apparatus ofclaim 1, wherein the controller is programmed to: operate the drivingcircuit to increase the frequency of the driving signal generated by thedriving circuit by a first amount; and operate the driving circuit todecrease the frequency of the driving signal generated by the drivingcircuit by a second amount.
 10. The apparatus of claim 9, wherein thefirst amount is the same as the second amount.
 11. The apparatus ofclaim 9, wherein the first amount or the second amount varies over time.12. The apparatus of claim 9, wherein the first amount or the secondamount is between 1 Hz and 1000 Hz.
 13. The apparatus of claim 1,wherein the source of negative pressure comprises a piezoelectric pumpor a micropump.
 14. The apparatus of claim 1, wherein the drivingcircuit comprises an H-bridge circuit.
 15. The apparatus of claim 1,further comprising the wound dressing, the source of negative pressurebeing disposed on or within the wound dressing.
 16. A method ofoperating a negative pressure wound therapy apparatus, the methodcomprising: supplying a driving signal to a source of negative pressureto power the source of negative pressure, the driving signal having amagnitude and a frequency, wherein the driving signal comprises anelectrical current or an electrical voltage; providing negative pressurevia a fluid flow path to a wound dressing with the source of negativepressure responsive to the driving signal; determining the magnitude ofthe driving signal at a first time and the magnitude of the drivingsignal at a second time subsequent to the first time; determining thatthe magnitude of the driving signal at the first time is less than themagnitude of the driving signal at the second time; in response todetermining that the magnitude of the driving signal at the first timeis less than the magnitude of the driving signal at the second time,increasing the frequency of the driving signal supplied to the source ofnegative pressure; determining the magnitude of the driving signal at athird time and the magnitude of the driving signal at a fourth timesubsequent to the third time; determining that the magnitude of thedriving signal at the third time is greater than the magnitude of thedriving signal at the fourth time; and in response to determining thatthe magnitude of the driving signal at the third time is greater thanthe magnitude of the driving signal at the fourth time, decreasing thefrequency of the driving signal supplied to the source of negativepressure.
 17. The method of claim 16, wherein said increasing thefrequency of the driving signal comprises increasing the frequency ofthe driving signal by a first amount; and said decreasing the frequencyof the driving signal comprises decreasing the frequency of the drivingsignal by a second amount.
 18. The method of claim 17, wherein the firstamount is different from the second amount.
 19. The method of claim 17,wherein the first amount or the second amount is between 1 Hz and 1000Hz.
 20. The method of claim 16, wherein the source of negative pressurecomprises a piezoelectric pump.